1. Field of the Invention
The present invention relates to strains of Drechslera monoceras having herbicidal activity against barnyard grasses at temperatures ranging from 26.degree. C. to 35.degree. C. and weed control compositions containing the same as an active ingredient.
2. Description of the Related Art
Environmental pollution caused by synthetic agricultural chemicals has become a modern social problem. As a result, new herbicides utilizing natural microorganisms are being touted as a new type of agricultural chemical which will not pollute the environment. For example, DeVine (effective component: Phytophthora palmivola) is commercially available in the United States as a weed control composition for strangle vine, a weed of family Asclepiadaceae, and Collego (effective component: Colletotrichum gloeosporioides), BioMal (effective component: Colletotrichum gloeosporioides f.sp. malvae) and LuboaII (effective component: Colletotrichum gloeosporioides f. sp. cuscutae) are commercially available as a weed control agent for northern jointvetch, a leguminous weed, in the United States, Canada and China, respectively.
No herbicides, that utilize living cells, are currently registered as agricultural chemicals in Japan. However, research is being done on the effect of mycoherbicides on weeds in rice paddies or lawns (Integrated Management of Paddy and Aquatic Weeds in Asia. FFTC Book Series No. 45, 1994). In particular, intensive research on mycoherbicides for barnyard grasses, which is a troublesome weed in rice cultivation, is being performed and it is reported in Japanese Patent Laid-open No. 1991/219883 (kokai 3-219883), Japanese Patent Laid-open No. 1994/329513 (kokai 6-329513) and others that a strain of genus Drechslera, which is a plant pathogen, is effective for controlling weeds of genus Echinochloa. However, such research has not reached the stage of practical applications.
Wild species of barnyard grasses are known as weeds in rice cultivation regions of the world, particularly in Japan, where they have long been regarded as troublesome weeds. According to Yabuno (Zasso Kenkyu (Weeds Research), volume 2, 1975), six species of wild barnyard grasses are known in the world, i.e., Echinochloa oryzicola, E. colona, E. pyramidalis, E. stagnina, E. haploclada and E. crus-galli. This latter species is further divided into three varieties, i.e., E. crus-galli var. formosensis, E. crus-galli var. crus-galli and E. crus-galli var. pratycola. Barnyard grasses known as troublesome weeds in rice cultivation are considered to be those produced by the natural crossing of plants between different species or subspecies of genus Echinochloa. A mycoherbicide to control barnyard grasses must have herbicidal activity against plants of all species and subspecies of genus Echinochloa, but must have no pathogenicity in major crops including rice. Further, weeds of genus Echinochloa start to germinate at 10.degree. C. and grow vigorously over a broad range of temperatures ranging from 15.degree. C. to 35.degree. C. Therefore, a mycoherbicide to control barnyard grasses should preferably have selective herbicidal activity against weeds of genus Echinochloa over a broad range of temperatures from a low of about 15.degree. C. to a high of about 35.degree. C.
Strains of mold fungi isolated from plants of genus Echinochloa, Drechslera monoceras IFO-9619 and IFO-9800, are stored at the Institute for Fermentation in Osaka. However, as explained below, these strains have no herbicidal activity against barnyard grasses known as troublesome weeds in rice cultivation.
Strains of Drechslera monoceras having herbicidal activity against barnyard grasses, such as MH-9011 (FERM BP-3416) are described in Japanese Patent Laid-open No. 1992/226905. However, as explained below, these strains have herbicidal activity against barnyard grasses at normal temperatures, i.e., about 25.degree. C., but almost no activity at temperatures above 30.degree. C.
The reality is that many species other than barnyard grasses grow in rice paddies and croplands, and these weeds also have to be controlled in rice cultivation. The general practice today is to apply several herbicides effective on different weeds in combination or as a composition of mixture of a multiple number of herbicides. As a result, the use of synthetic agricultural chemicals has increased considerably. Application of large amounts of synthetic agricultural chemicals is creating not only concerns about pollution of the water, soil or the like, but is creating a vicious circle of inducing chemically-resistant weeds and insect pests or pathogens having drug resistance. Thus, there is an urgent need to develop new agricultural chemicals that are safe to humans and animals but do not pollute the environment. At the same time, enforceable measurements to reduce the use of synthesized agriculture chemicals are required.